1. The role of intestinal bacteria in health and disease.
Recent work into the role of intestinal bacteria in a variety of disease states including inflammatory bowel disease, obesity, and diabetes has established a clear link between these bacteria and our health. The Britton laboratory is focused on two areas of research in this area: the role of probiotic bacteria in treating disease and the role of the intestinal microbiota in preventing pathogen invasion.

Probiotic Lactobacillus reuteriMuch of our work focuses on characterizing how different strains of Lactobacillus reuteri impact various aspects of the host response including inflammation, bone health, pathogen invasion and intestinal function. We use a variety of in vitro and animal models to explore how L. reuteri impacts health. Our overall goals are to identify novel probiotic strains that can be used to prevent or ameliorate disease and to develop a platform for the delivery of biotherapeutics.

Microbiota and prevention of pathogen invasion. We are interested in understanding how the intestinal microbiota provides a barrier to incoming pathogens and how perturbations of the microbiota result in an established infection. We have focused most of our attention on the pathogen Clostridium difficile, which is the most common cause of antibiotic associated diarrhea and is quickly becoming the most common cause of nosocomial infections. We have developed mini-bioreactors and mice colonized with a human intestinal microbiota to address which members of the community are responsible for inhibiting C. difficile invasion. Our ultimate goal is to develop a probiotic cocktail derived from the human intestinal microbiota that will suppress C. difficile invasion.

This project is funded by the NIH Enteric Research Investigative Network (ERIN). The Michigan State University ERIN is directed by Linda Mansfield with myself and Shannon Manning as project leaders.

Collaborators: Much of the work we do is interdisciplinary and thus we engage in a number of collaborative projects. Our collaborators include Laura McCabe (Michigan State University), Nara Parameswaran (Michigan State University), Vincent Young (University of Michigan), James Versalovic (Baylor College of Medicine), Stefan Roos (Swedish University of Agricultural Sciences), Eamonn Connolly (Biogaia AB), Linda Mansfield (Michigan State University), Shannon Manning (Michigan State University), Kathryn Eaton (University of Michigan).

2. Recombineering in lactic acid bacteria. Recombineering technology allows for the precise genetic manipulation of bacterial chromosomes. Using single-stranded DNA (ssDNA) recombineering technology point mutations, small deletions, and small insertions can be recovered without the need for selection. Previous to our recent work, non-selected ssDNA recombineering could only be performed in Escherichia coli. We have now established non-selected recombineering in two lactic acid bacteria strains, Lactobacillus reuteri and Lactococcus lactis. We also have shown that recombineering can function in other Gram-positive bacteria as well. We can achieve average recombineering efficiencies of ~15% in L. lactis, which will now enable directed evolution of multiple chromosomal sites to be achieved simultaneously. Finally, we have also developed an efficient method for inserting genes stably into the chromosome of L. reuteri, which will enable the use of this human-derived organism to be used in the intestinal delivery of biotherapeutics and vaccines.L. reuteri.

3. GTPase control of ribosome assembly. GTPases play an important role in the assembly of ribosomes in all three kingdoms of life. The molecular mechanisms by which they function are largely unknown. We are studying the ribosome assembly GTPase RbgA in Bacillus subtilis in an attempt to understand how these proteins act in the maturation of the large ribosomal subunit using a combination of biochemical, structural and genetic approaches. Interestingly, mutation or depletion of RbgA results in the accumulation of a ribosome assembly intermediate that is arrested at a very late stage of development. Work on eukaryotic homologs of RbgA suggests that these proteins are involved in a late assembly step of the large ribosomal subunit. The results from this bacterial work will have important implications for the formation of cytoplasmic, mitochondrial, and chloroplast ribosomes.

FundingWe are grateful to the following funding agencies for current and past support of our research: NIH, NSF, DARPA, Michigan State University Foundation, Gerber Foundation, Michigan State University Vice President for Research Office, Biogaia AB, Christian Hansen, Novozymes, Procter and Gamble, Michigan State University Department of Microbiology and Molecular Genetics.